A host of options in mixed martial arts also await McGregor. The power-punching cage fighter is set to return to the UFC octagon in December and could face Khabib Nurmagomedov, Tyron Woodley, or Nate Diaz.

"I thought the Forbes list ran from January to December but it's July to July. I wanted the number one spot this year but I said I'd fight on December 30 so I'm still going to fight. I'm an active mother f*****."

2) Tailor-made for the fashion game

David August. David August screenshot McGregor, wearing an x-rated three-piece suit, also announced a clothing line he is launching in collaboration with renowned California-based tailor David Heil, founder of David August. McGregor hopes his brand ends up toppling luxury designer fashion label Net-A-Porter.

"My suit says 'f*** off' on the pinstripe — that's a cracker," McGregor said. "My suit tailor David August came up with a line of suits; August McGregor.

"[It's] not just suits, [it will be] clothes right down. Jeans, pants, the whole lot. They'll be in retail stores and we'll build an online shopping site to rival Net-A-Porter, who makes $66 million profit a year.

"I love fashion and I get to design clothes. It's like fighting, it's all about the small details."

The Irishman is free to strike deals beyond his usual UFC contract for the Mayweather fight and could therefore substantially increase his earnings.

Can McGregor realistically top the Forbes rich list?

McGregor is currently ranked 24 on the Forbes list of highest-paid athletes. This is a notable improvement on his 2016 rank of 84 but he would still need a 173% pay increase to topple the current number one Cristiano Ronaldo.